Single user can't purchase any in-app item.

### Platform

- [x] iOS
- [ ] macOS
- [ ] tvOS

### In app purchase type

- [ ] Consumable
- [x] Non-consumable
- [ ] Auto-Renewable Subscription
- [ ] Non-Renewing Subscription

### Environment

- [x] Sandbox
- [x] Production

### Version
Latest

### Related issues
ℹ Please replace this with references to similar issues (either open or already closed).

## Report

A single user of mine is unable to purchase any product from me.

### What did you expect to happen
I expected them to be prompted for their login details but they never are.

I am using the most basic function `SwiftyStoreKit.purchase`